Zhang Xiulin, Zhu Chongbin, Xu Shaofen, Cao Xiaoding, Wu Gencheng, Li Moyi, Cui Dafu, Chi Chengwu. Effect of intrathecal or intracerebroventricular administrition of ofq on pain threshold and acpuncture analgesia in rats. Acta Physiol Sin 1997; 49 (5): (in Chinese with English abstract).